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Identification and reactivity of the triplet excited state of 5-hydroxytryptophan

Dad, S, Bisby, RH, Clark, IP and Parker, AW 2005, 'Identification and reactivity of the triplet excited state of 5-hydroxytryptophan' , Journal of Photochemistry and Photobiology B: Biology, 78 (3) , pp. 245-251.

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Abstract

Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence (‘hyperluminescence’). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (λmax 400-420 nm) and another transient absorption with λmax 480 nm and lifetime of 2 μs in deaerated solutions. Based on quenching by oxygen and β-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with λmax 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen (1O2*) with a quantum yield of ∼0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 × 108 dm3 mol-1 s-1. The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin.

Item Type: Article
Themes: Subjects / Themes > Q Science > Q Science (General)
Subjects outside of the University Themes
Schools: Colleges and Schools > College of Science & Technology
Colleges and Schools > College of Science & Technology > School of Environment and Life Sciences
Colleges and Schools > College of Science & Technology > School of Environment and Life Sciences > Biomedical Research Centre
Journal or Publication Title: Journal of Photochemistry and Photobiology B: Biology
Publisher: Elsevier
Refereed: Yes
ISSN: 10111344
Depositing User: H Kenna
Date Deposited: 08 Aug 2007 11:52
Last Modified: 20 Aug 2013 16:45
URI: http://usir.salford.ac.uk/id/eprint/171

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